This invention relates to a beam waveguide for coupling energy from a stationary beam source into a rotatable-reflector antenna.
In one type of directional antenna system, a signal to be transmitted is generated from a source, directed against a front face of a reflector, and projected through free space by reflection from the reflector. The reflector is typically parabolic in shape, so that the signal directed against it from its focus is projected as a parallel beam. Variations in this basic approach, such as the Cassegrain antenna employing a main reflector and a subreflector, have been developed.
The aiming of the signal emanating from the antenna is accomplished by pointing the reflector in the desired direction. One approach to pointing the antenna is to mount the antenna on a rotational mechanism. The rotational mechanism may be of any type, but one common structure uses a gimbal that permits the antenna reflector to be pointed in any direction of a hemisphere.
Two important problems in the design of an antenna having the gimbaled antenna reflector are coupling the signal from the signal source to the reflector and minimizing the signal loss between the signal source and the reflector. In one straightforward approach, the source is affixed to the antenna reflector and must be supported and moved by the gimbal mechanism. This approach is not desirable for most antenna systems due to the weight and bulk of the source, which in turn require that the gimbaling mechanism be larger and heavier than desirable.
Responsive to this problem, antenna systems have been developed wherein the transmitting tube is fixed, and a waveguide extends from the transmitting tube to the feed horn. The feedhorn is mounted to the antenna reflector and is therefore movable with the reflector. The waveguide has one or more rotary joints to allow the feed horn to rotatably move with the antenna reflector. This approach is operable, but signal losses in the rotary joints, especially at millimeter wave frequencies, are high.
In a further improvement, a beam waveguide using reflective elements has been developed and is in use with deep-space radio telescopes. This approach will be discussed more fully subsequently, but for most applications it requires that a high-gain feed be used. If a lower gain feed is used with magnification of the source, the feed pattern is corrupted.
There is a need for a beam waveguide and antenna system that can utilize a low-gain feed without corrupting the feed pattern purity. The present invention fulfills this need, and further provides related advantages.